1. Field of the Invention
The present invention relates to an organic photoreceptor (hereinafter, also referred to simply as “photoreceptor”) for use in electrophotographic image formation, and an image forming apparatus including the organic photoreceptor, and an image forming method.
2. Description of the Related Art
Organic photoreceptors have been considered as the mainstream on behalf of inorganic photoreceptors, because the organic photoreceptors have advantages such as the expanded scope of material selection, excellent environment adaptability, and low production cost, as compared with inorganic photoreceptors like selenium photoreceptors and amorphous silicon photoreceptors.
In recent years, highly-durable photoreceptors have been desired in response to image forming apparatuses which have improved in speed and image quality.
In general, photoreceptors have a problem that the surfaces of the photoreceptors are abraded by contact with cleaning unit such as a blade. In order to suppress the abrasion of the photoreceptor surfaces, it is known that a protective layer is provided on the photoreceptor surfaces (see, for example, JP 2008-46198 A).
Conventionally, cured resins obtained by the polymerization of polymerizable compounds, which contain metal oxide microparticles surface-treated with a surface preparation agent having a reactive organic group, have been known as protective layers which are excellent in abrasion resistance and scratch resistance (see, for example, International Publication WO 2010/018725).
However, the protective layers from the cured resins containing the metal oxide microparticles have the problem of decreased dot reproducibility, because of diffusion caused during hole transfer at reduced electric field intensity. Furthermore, the protective layers from the cured resins containing the metal oxide microparticles are excellent in abrasion resistance, and thus able to have longer lifetime, but at the same time, have problems such as transfer memory generation and decreased dot reproducibility, due to the decrease in surface resistance under high-temperature and high-humidity environments, with discharge products deposited on the photoreceptor surfaces in the latter halves of the useful lives of the photoreceptors.
The method of adding a charge transport substance to the protective layer is conceivable in order to suppress the generation of transfer memory. However, as the additive amount of the charge transport substance is increased, the problem of decreased dot reproducibility is newly caused while the suppression effect of transfer memory generation is increased. Furthermore, as the additive amount of the charge transport substance is increased, the charge transport substance develops a function as a plasticizer, thereby causing a problem that the protective layer fails to have high film strength (scratch resistance).